Cutaneous tuberculosis (TB) is essentially an invasion of the skin by Mycobacterium tuberculosis, the same bacteria that cause TB of the lungs (pulmonary TB).  Cutaneous TB is a relatively uncommon form of extrapulmonary TB (TB infection of other organs and tissues). Even in countries such as India and China where TB still commonly occurs, cutaneous outbreaks are rare (<0.1%).

1. Cutaneous tuberculosis
Cutaneous tuberculosis (TB) is essentially an
invasion of the skin by Mycobacterium
tuberculosis, the same bacteria that cause TB of
the lungs (pulmonary TB).
Cutaneous TB is a relatively uncommon form of
extrapulmonary TB (TB infection of other organs
and tissues). Even in countries such as India and
China where TB still commonly
occurs, cutaneous outbreaks are rare (<0.1%).

2. Types of cutaneous TB
• Several different types of cutaneous TB exist.
• Direct infection of the skin mucous membranes
from an outside source of Mycobacteria results in
an initial lesion called the tuberculous chancre.
The chancres are firm shallow ulcers with a
granular base. They appear about 2-4 weeks after
mycobacteria enter through broken skin. The
immune response of the patient and the virulence
of the Mycobacteria determine the type and
severity of cutaneous TB.

3. Erythema induratum
Innoculation Tuberculosis
(Also Tuberculid Infection)

4. TB verrucosa cutis
Features:
Occurs after direct inoculation of
TB into the skin in someone who
has been previously infected
with mycobacteria
Presents as a purplish or
brownish-red warty growth
Lesions most often occur on the
knees, elbows, hands, feet and
buttocks
Lesions may persist for years but
can clear up even without
treatment

5. Lupus vulgaris
Persistent and progressive
form of cutaneous TB.
Small sharply defined
reddish-brown lesions
with a gelatinous
consistency (called apple-
jelly nodules)
Lesions persist for years,
leading to disfigurement
and sometimes
skin cancer.

6. Scrofuloderma
Skin lesions result from direct
extension of underlying
TB infection of lymph nodes,
bone or joints
Often associated with TB of the
lungs
Firm, painless lesions that
eventually ulcerate with a
granular base
May heal even without
treatment but this takes years
and leaves unsightly scars

7. Miliary TB
Chronic TB infection that has spread from the
primary infection (usually in the lungs) to other organs
and tissues via the bloodstream
Skin lesions are small (millet-sized) red spots that
develop into ulcers and abscesses
More likely in immunocompromised patients, eg HIV,
AIDS, cancer
The patient is generally sick
Prognosis is poor (many patients die even if diagnosed
and treated)

8. Tuberculid
Generalized exanthem in patients with moderate or high
degree of immunity to TB because of previous infection
Usually in good health with no identifiable focus of
active TB in skin or elsewhere
Erythema induratum (Bazin disease) presents as
recurring nodules or lumps on the back of the legs
(mostly women) that may ulcerate and scar. It is a type
of nodular vasculitis.
Papulonecrotic tuberculid results in crops of recurrent
crusted skin papules on knees, elbows, buttocks or lower
trunk that heal with scarring after about 6 weeks.
Lichen scrofulosorum is an extending eruption of
small follicular papules in young persons with underlying
TB.

9. Diagnostic TESTS tests are available?
The diagnosis is usually made or confirmed
by characteristic histopathological features on skin biopsy.
Typical tubercles are caseating epithelioid granulomas that
contain acid-fast bacilli. These are detected by tissue
staining, culture and polymerase chain reaction (PCR).
Other tests that may be necessary include:
Tuberculin skin test (Mantoux or PPD test)
Interferon gamma release assay blood test
Sputum culture (it may take a month or longer for results to
be reported)
Chest X-ray and other radiological tests for
extrapulmonary infection.
Interferon gamma release assays (IGRA)

10. PPD skin test
The PPD skin test is a method used to diagnose silent (latent) tuberculosis (TB)
infection. PPD stands for purified protein derivative.
How the Test is Performed
The patient will need 2 visits to doctor's office for this test.
At the first visit, the health care provider will clean an area of patient’s skin, usually
the inside of the forearm. He/ She will get a small shot (injection)
that contains PPD. The needle is gently placed under the top layer of skin, causing a
bump (welt) to form. This bump usually goes away in a few hours
as the material is absorbed.
After 48 to 72 hours, the patient must return to the health provider's office. The health
provider will check the area to see if the patient have had a strong reaction to the test.

11. Treatment of cutaneous TB
Patients with pulmonary or extrapulmonary TB
disease need to be treated with anti-tubercular
drugs. This usually involves a combination of
antibiotics (isoniazid, rifampicin, pyrazinamide and
ethambutol) given over a period of several months
and sometimes years.
Patients with latent TB infection but no active
disease may also be treated with antitubercular
drugs to prevent development of active disease.
Occasionally surgical excision
of localised cutaneous TB is recommended.